This invention relates to a pneumatic control apparatus for an interchangeably operable pneumatic device, which apparatus is equipped with a shut-off reversing valve for selectively shutting off and supplying a flow of compressed air to the pneumatic device to achieve each of two movements, and is equipped with a pressure reducing valve for restricting the pressure to a determined pre-selectable value.
Pneumatic control apparatus of this type have been known for a long time. In particular, in the case of so-called direct controls, i.e. in which the power flow supplied to the pneumatic device is subjected to a control, the shut-off reversing valve and the pressure reducing valve are in different locations. This applies, in particular, to arrangements in which the shut-off reversing valve is suspended from a device as an operational unit, as for example in the case of pneumatic lifting trains or pneumatically operated shunting trolleys on monorail conveyors. Since, moreover, in the case of direct controls, the members to be handled by the staff have to be of a relatively large and bulky design, the accommodation of the pressure reducing valve in the vicinity of the shut-off-reversing valve is still extremely undesirable, because in that case, the operational apparatus is even more unwieldy.
However, in the case of the control of considerable capacities, delays are caused due to the lines which are present as a result of the distance between the two valves, which delays may have a negative influence on the response behaviour and, in some cases, may also result in oscillations in the control system. In such an event, it may happen that the pre-selected pressure value is exceeded for a short time, which is particularly undesirable for safety reasons.